The simplest kind of such roller blind devices are, e.g., the known bolt spring rollers or snap rollers. In these devices a torsional spring is arranged in the fabric shaft and an engagement mechanism for different roll-off lengths of the fabric is provided. These roller blinds require a significant amount of force for operation and frequently snap upward in an undesired manner. In addition, roller blinds with cord tensioning devices are known. In these instances the cord is rolled up onto a second shaft. The cord shaft is driven by torsional spring in the cord shaft. Even these devices require a great amount of force and exert a heavy load on the structural components.
Furthermore, generic roller blind devices constitute the subject matter of EP 0 483 528 A1 and of WO 01/53647 A1 as well as of GB 2 166 480 A. Similar devices are also disclosed in the publications EP 0 154 218 A2, EP 0 795 674 A2 and DE 4 342 977 A1 as well as DE 197 37 632. These publications describe roller blind devices with a fabric that can be wound onto a rotationally drivable fabric shaft mounted on a frame in which a pull rod is arranged on the free edge of the fabric onto which rod a force acts in the direction of the drawing off of the fabric. In the cited publications this force is generated either manually or by an electric motor and various diversions of the pull cords acting on the pull rod are provided.
The considerable insertion dimensions necessitated by the construction are disadvantageous in the known solutions. An insertion into customary double-glass windows with a 16 mm glass interval is possible with these devices, but a significant part of the original window area is lost, which reduces the incidence of light since a significant frame width is necessary for covering the functionally important parts. Moreover, a significant motor power with corresponding current consumption and corresponding heat waste, as well as large construction dimensions, are required, also necessitated by the design. Finally, these devices have a very complex mechanism and control, require many structural components and are therefore expensive, complicated, and have a high manufacturing cost.
Finally, publications DE 38 36 595 A1 and DE 9001090 U of the applicant teach windows and/or devices for darkening windows in which several rollers are connected to each other by a transmission, and a darkening web covering only part of the window can be wound ontoto each roller. These devices are operated with flexible rubber cords or springs in the pull device. They have the disadvantage that a rubber cord pull is a critical construction element, since the rubber eventually becomes brittle and tears. In the spring arrangement, the guidance around a cam is problematic.
DE 92 15 788 U1 and DE 87 03 605 U1 each show a roller blind device designed as a counterpull roller with a fabric that can be wound ontoto a rotationally drivable fabric shaft mounted on a frame and with a pull rod arranged on the free edge of the fabric onto which rod a force acts in the direction of the drawing off of the fabric. A cord reel is connected coaxially and in a prolongation of the fabric shaft to each side of the fabric shaft in such a manner that it rotates in unison with it and the free end of each cord that can be wound onto the shaft is connected to the pull rod via a cord deflection, as a result of which the cord is wound ontoto the cord reels when the fabric is pulled from the fabric shaft and vice versa. At least one spring arrangement is provided in the course of the cord or cords for adapting the length of the cord to the varying winding state of the fabric shaft and of the cord reels. This spring arrangement can be arranged inside the pull rod.
Furthermore, DE 296 09 604 U1 shows a roller blind device provided for insertion into an insulating window and comprising a laterally arranged pulley and counterweight instead of springs.
These publications have the disadvantage that two cord reels are used and, in the case of different left and right winding diameters, straight guidance of the fabric or of the pull rod is no longer possible. Furthermore, only one helical spring is provided for both cords, which significantly limits the spring travel. The described arrangements can shade only windows that are wide but not very high (e.g., automobile panes). These arrangements are not suitable for long and narrow panes, e.g., for terrace doors or roof area windows. Since the length of the usable spring travel is limited by the width of the entire device, only a correspondingly short spring travel is available when only one spring is used. Thus, however, a sufficient compensation of the different winding diameters of the fabric shaft and the cord rollers in correspondingly high windows is not possible. The pull rods described in the publications also do not make it possible to introduce two springs with added spring travel.
There is therefore the problem of further developing a generic roller blind device in such a manner that a compact construction is achieved that only minimally reduces the incidence of light through the window and that even high and narrow windows can be provided with the device. There is furthermore the problem of making available a pane of insulating glass provided with such a roller blind device and a corresponding window. These problems are solved by the characterizing features of Claim 1 and by the features of Claims 13 and 14.